1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of manufacturing a semiconductor capacitor having a hemispherical grain (HSG) layer.
2. Description of the Related Art
As semiconductor devices such as DRAMs have become more highly integrated, the area available in the DRAM for a capacitor used for storing data has gradually become smaller while the capacitance requirements have increased. Therefore, various ways have been studied to realize a capacitor having a large capacitance in a small area.
For instance, ways to maximize the surface area of a capacitor within a given space have been studied as means for counteracting the reduction in storage capacitance that would otherwise accompany a reduction in the overall size of the capacitor. These studies include a method of forming a hemispherical grain (HSG) layer on a surface of a storage electrode of the capacitor during its manufacture, to increase the effective surface area of the capacitor.
The conventional process of manufacturing a capacitor having an HSG layer will be briefly described. First, a contact hole is formed in an insulating layer disposed on a semiconductor substrate. The contact hole will be used to connect the capacitor to an active region of the semiconductor substrate. Amorphous silicon is then deposited over the entire surface of the resultant structure. Then, a storage electrode pattern of the capacitor is formed from the amorphous silicon using a well-known photo etching process. Subsequently, an HSG layer is formed by depositing seed particles on the exposed surface of the storage electrode pattern, and controlling the temperature of the seed particles to thereby grow the particles at the surface of the storage electrode pattern, whereby the effective surface area of the storage electrode pattern is increased. Next, a dielectric layer is formed on the HSG layer, and material is deposited and patterned on the dielectric to form a plate serving as the upper electrode of the capacitor.
Not only is the process of forming the HSG layer very complicated, but the growth of the HSG seed layer is much affected by the condition of the exposed surface of the storage electrode pattern. Accordingly, in the prior art, the exposed surface of the storage electrode pattern is cleaned by a wet cleaning process before the HSG layer is formed, to eliminate etching residue, particles, and organic pollutants that remain after the etching process for forming the storage electrode pattern is performed. A mixture of a standard cleaning solution #1 (SC-1) developed by the RCA company and a diluted hydrofluoric acid (DHF) is used as a cleaning solution. The SC-1 is mainly used for eliminating particles or organic pollutants existing on the surface of the wafer. The DHF has a function of eliminating a natural oxide layer as well as a heavy metal.
However, if such a wet cleaning process is performed on a pattern, in which a polysilicon layer and an oxide layer are simultaneously exposed, the oxide layer is inadvertently and undesirably etched. A dry cleaning process using isopropyl alcohol (IPA) is performed to eliminate moisture after the wet cleaning process is performed. However, this process can leave a defect such as a water mark, which can adversely affect the reliability of the device and the production yield. Preventing the defect from occurring, especially in the case where an anti-reflection film such as an SiON film is used for forming the storage electrode pattern, has its limits.
Meanwhile, the device is subjected to the wet cleaning process again after the HSG layer is formed in an attempt to eliminate such a defect before the dielectric layer is formed. However, in this case, the HSG layer is etched by the wet cleaning process, thereby reducing the capacitance of the capacitor. Moreover, the HSG layer can be excessively etched to the point where hemispherical grains separate from the remainder of the HSG layer.
Still further, if the wet cleaning process is performed in a process chamber different than that used for forming the HSG layer or the dielectric layer, the HSG layer or the dielectric layer can be contaminated or undesirable layers such as a natural oxide layer can be formed during the transfer of the device to the process chamber for forming the HSG layer or dielectric layer, even though the surface of the storage electrode or the HSG layer is cleaned by the wet cleaning process. As a result, the dielectric efficiency of the capacitor is decreased.
An object of the present invention is to provide a method of manufacturing a semiconductor device including a cleaning process that will optimize the growth of an HSG layer constituting a storage electrode of the device.
To achieve this object, a method of manufacturing a semiconductor device according to the present invention includes a step of dry cleaning an exposed surface of a polysilicon pattern, on which the HSG layer is to be grown, using hydrogen in a plasma state and a fluorine-based gas. First, a polysilicon layer is formed on a semiconductor substrate. Next, a polysilicon pattern, at least a portion which is exposed, is formed by etching the polysilicon layer. Subsequently, the exposed surface of the polysilicon pattern is dry cleaned by supplying the hydrogen in a plasma state and the fluorine-based gas towards the exposed surface of the polysilicon pattern. Preferably, the exposed surface of the polysilicon pattern is also wet cleaned to remove any pollutants produced as the result of the etching process. The HSG layer is then formed on the cleaned surface of the polysilicon pattern.
During the dry cleaning process, the hydrogen in a plasma state and the fluorine-based gas chemically react with an oxide layer formed on the exposed surface of the polysilicon pattern to form a reaction layer. The dry cleaning process also preferably includes annealing the reaction layer to thereby vaporize and eliminate the reaction layer. The wet cleaning can be performed using ozone water or a standard cleaning solution (SC-1).
It is another object of the present invention to provide a method of manufacturing a semiconductor device, including a cleaning process, which prevents contaminants from remaining on layers of the device, such as an HSG layer and/or a dielectric layer.
To achieve the second object, a method of manufacturing a semiconductor device according to the present invention employs wet and dry cleaning processes before and after the forming of the HSG layer. First, a polysilicon layer is formed on a semiconductor substrate. Next, a polysilicon pattern, at least a portion which is exposed, is formed by etching the polysilicon layer. Subsequently, the exposed surface of the polysilicon pattern is wet cleaned to remove any pollutants produced as the result of the etching process. The surface is then dry cleaned by supplying hydrogen in a plasma state and fluorine-based gas towards the exposed surface of the polysilicon pattern. The HSG layer is then formed on the cleaned surface of the polysilicon pattern. Subsequently, the HSG layer is wet cleaned to remove any pollutants remaining thereon. The surface is then dry cleaned by, again, supplying hydrogen in a plasma state and fluorine-based gas towards the surface of the HSG layer. Finally, a dielectric layer is formed on the cleaned surface of the HSG layer.
According to the present invention, any pollutant or an oxide layer remaining on the storage electrode surface is chemically reacted with hydrogen in a plasma state and fluorine-based gas. The reactant can thus be easily removed by an annealing process. The condition of the surface therefore becomes optimal for growing the HSG layer thereon. Moreover, any pollutant or oxide layer remaining on the HSG layer is also chemically reacted with hydrogen in a plasma state and fluorine-based gas and thus, such a reactant can also be easily removed by an annealing process. The HSG layer is not degrade by such a gentle cleaning process. Furthermore, the cleaning process, subsequent formation of the HSG layer and of the dielectric layer can be readily carried out in a clustered facility, whereby the cleaned surface is effectively prevented from being re-contaminated. thus, highly reliable semiconductor devices can be manufactured.